Thanks everyone. The prevailing opinion seems to be a "b" oddly shaped that it is.
Dave Baird states above that the letter suffix was changed every set of 10,000.
According to cruffler.com/historic-may01.html:
"WaA140: This stamping was used from late 1941 to the liberation in 1944 on approximately 325,000 7.65mm pistols. Serialization began in the 67,000 - 68,000 range and proceeded to approximately serial number 155,000. In late 1943 serialization was restarted using the German military system. In this system serial numbers were limited to five digits with a one letter suffix. The letter indicated a block of 100,000 pistols. (Example: A pistol with the serial number 34554b is actually the 234,554th pistol produced - the first block of 100,000 had no suffix, pistols 100,000 - 199,999 were suffixed with an a, and pistols 200,000 through 299,999 were suffixed with a b.) In 1944, serial number markings were simplified with the full serial number appearing only on the slide, with the last four digits appearing on the frame."
If indeed it was changed every set of 100,00 with a production of only 325,000 they should not have gotten higher than a "c" suffix.
By my math I see it as:
001 to 99,999 - no letter suffix
100,000 to 199,999 - "a" suffix
200,000 to 299,999 - "b" suffix
300,000 to end - "c" suffix
If the above quote is accurate, with mine having the full serial number on the slide (x3912b) and last 4 on the frame, I believe it to be 1944 production, specifically 2x3912. Does this sound accurate?
Bayoned - You said you have this same shaped "b" on your FN 1922's?